Silver as a Cure for Ebola - Literature Collection

International Journal of Microbiological Research 1 (1 ): 33-36, 201 0

ISSN 2079-2093

© IDOSI Publications, 2010

Colloidal Silver as a New Antimicrobial Agent

Nouran H. Assar and HayamM. Hamuoda

Department of Microbiology,
National Organization for Drug Control and Research (NTODCER), Giza, Egypt

Abstract: Silver has the advantage of having broad antimicrobial activities against Gram-negative and
Gram-positive bacteria. This research was the result of bioassay experimentation on the effects of colloidal silver
on multidrug resistant bacteria. The initial idea was to determine the antimicrobial activity of colloidal silver.
So it could be used as a powerful in-vitro antimicrobial agent. Antimicrobial activity was determined by means
of agar diffusion. Resistant clinical isolates of Staphylococcus aureus, Escherichia coli, pseudomonas
aregnosa and Salmonella typhi were used as the test organisms. It was concluded this study showed
successful formation of colloidal silver and their antibacterial activity against all tested pathogens.

Key words: Antimicrobial activity • Silver • Bacteria

INTRODUCTION

The emergence and spread of antibiotic resistance
is an alarming concern in clinical practice. Increasingly,
agents with 'antimicrobial' effects are being coated on
materials and medical devices [1] as a prophylaxis to
prevent bacteria from growing or for therapeutic use.
The new technology of impregnation of silver
nanoparticles [2] is enabling a wider range of these
medical products to be available to clinicians. The use
of metallic silver as an antimicrobial agent has long been
recognized [3, 4]. Dilute solutions of silver nitrate had
been used since the 19 th century to treat infections and
burns before the introduction of silver sulphadiazine
cream [5].

Silver has the advantage of having broad
antimicrobial activities against Gram-negative and
Gram-positive bacteria and there is also minimal
development of bacterial resistance [6].

The antimicrobial activity of silver has been
recognized by clinicians for over 100 years [4]. In addition,
many reports suggested that hygienic benefits have been
associated with the use of silver for considerably longer
time. In the same time, records showed that Hippocrates
recognized the role of silver in the prevention of disease
and the Romans stored wine in silver vessels to prevent
spoilage. However, only in the last few decades the
mode of action of silver as an antimicrobial agent has
been studied without any rigour [7]. Silver nano-particles

have also been demonstrated to exhibit antimicrobial
properties both against bacteria [8] and viruses [9] with
close attachment of the nano-particles themselves with
the microbial cells / virus particles being demonstrated
with activity being size dependent [9]. Despite this, the
principle activity of silver is as results of the production
of silver ions within an aqueous matrix [10]. This therefore
implies that for silver to have an antimicrobial effect,
free water must be present. Interruption of cell wall
synthesis resulting in loss of essential nutrients has
been shown to occur in yeasts [11] and may well occur in
other fungi. Antiviral activity of silver ions has been
recorded and interaction with -SH groups has been
implicated in the mode of action. The association of silver
nano-particles with the envelope of certain viruses has
been suggested to prevent them from being infective [9].

The current work was designed to throw lights on
the in vitro antibacterial activity of colloidal silver with
special emphasis on the comparison between silver
solutions, sulphonamides and trimethoprime alone or in
combination.

MATERIALS AND METHODS

Preparation of the Colloidal Silver Suspension in Pure
Water: Colloidal silver solution was electrically prepared.
Pure silver wires were used as both the positive and
negative electrodes. The pure silver wires were etched by
the DC pulse arc-discharge in pure water [1 2].

Corresponding Author: Nouran H. Assar, Department of Microbiology,

National Organization for Drug Control and Research (NODCER), Giza, Egypt

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Intl. J. Microbiol. Res., 1 (1): 33-36, 2010

Determination of Antibiotics Susceptibility (By Disc
Diffusion Method): The tested isolates were sub cultured
on nutrient agar plates for 24 hours at 37°C. 3-4 similar
colonies were selected and aseptically transferred into
5ml of Muller Hinton broth and incubated at 37°C for
4-5 hours. One ml of the previous suspension was
transferred to Muller Hinton agar tube and
homogeneously suspend using vortex then the mixture
was poured in a Petri dish and kept to dry for 1 0 minutes.
Antibiotic discs were applied using aseptic technique
with 1cm apart with gentle pressure to allow complete
diffusion.

The Antibiotic Discs Were Supplied from Oxoide
Company:

Chloroamphinicol © 30mcg
Cefaclor (Cj) 30mcg
Cefadroxil (Cfr)
Ciprofloxacin (Cf) 5mcg
Erythromycin (E) 1 5mcg
Levofloxacin (Le) 5mcg
Norfloxacin (Nx) 1 Omcg

Sulphonamides&Trimethoprime (Stx) 23.75/1 .25mcg
Tobramycin (Tb) 1 Qmcg
Incubate plates 24 hours at 37°C.

The diameter of the inhibition zones were measured
and compared to a reference table to differentiate the
isolates into sensitive, intermediate or resistant [13].
As shown in Table 1 .

RESULTS

Antimicrobial susceptibility test for different
antibiotic groups and sliver solution against four isolates
were determined using diffusion method (Table 1).

Table 2 shows that all tested bacteria were resistant
to more than one antibiotic. The important observation
was the antibacterial activity of colloidal silver against
Escherichia coli, Staphylococcus aureus, Salmonella
typhi and Pseudomonas aeruginosa which exhibit
superior effect compared with other antibiotics.

Figure 1 Showed the antimicrobial susceptibility test
for the different used antibiotic groups and sliver against
four isolates.

DISCUSSION

The emergence and spread of antibiotic resistance is
an alarming concern in clinical practice, Nanotechnology
is gaining tremendous impetus in the present century due
to its capability of modulating metals into their nanosize,

Table 1 Zone diameter interpretation charts forthe antibiotics used according to NCCL2007

Diameter of zone of inhibition in mm

Antibiotic Class

Antibiotic Name

Symbol

Disc content

Resistant mm or less <

Intermediate mm (I) Sensitive mm or more (S)

Amphenicols
Aminoglycosides
Betalactams
cephalosporins

Sulphon amides & Trimethoprime

Macrohdes

Quinolones

Chloroamphenicol C 30 meg

Tobramycin Tb 10 meg

Cefaclor Cj 30 meg

cefadroxil Cfr 30 meg

Sulphonamides & Trimethoprime Stx 23 75/1 25 meg

Erythromycin E 15 meg

Cibrofloxacin Cf 5 meg

Levofloxacin Le 5 meg

Norfloxacin Nx 10 meg

13-17

13- 14
15-17

15- 17
11-15

14- 22

16- 20
16-18
13-16

Table 2: Antimicrobial susceptibility test for different antibiotic group and sliver against four isolates

Diameter of zone of inhibition in mm of resistant Bacterial isolates

Antibiotic Name &

taphylococcus aureus

Pseudomonus aregnosa

Salmonella

yphi

Echerishia coli

Chi oro amph eni c ol

I

R

R

I

Tobramycin

R

S

I

R

Cefaclor

R

R

R

R

cefadroxil

R

R

R

R

Sulphonamides & Trimethoprime

I

R

R

R

Erythromycin

R

R

R

R

Cibrofloxacin

R

S

R

R

Levofloxacin

R

S

R

R

Norfloxacin

R

s

R

R

Silver

S

s

S

S

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Ml J. Microbiol. Res., I (1): 33-36, 2010

Fig. 1: Antimicrobial susceptibility test for the different used antibiotic groups and sliver against four isolates

which drastically changes the chemical, physical and
optical properties of metals. Metallic silver in the form of
silver nanopar tides has made a remarkable comeback as
a potential antimicrobial agent.

The present study showed successful formation of
colloidal silver and their antibacterial activity against
Escherichia coli (E. coli), Staphylococcus aureus
(S. aureus), Salmonella typhi (S. typhi) and
Pseudomonas aeruginosa (P. aeruginosa). Colloidal
silver showed a strong bactericidal effect against E. coli y
S. aureus and P. aeruginosa, these resuls were in
agreement with those reported by Bryaskova et ai. [14].

In the present experiment, colloidal silver showed
highly potent antibacterial activity toward both Gram-
positive and Gram- negative bacteria. This condition may
be due to its accumulation in the bacterial membrane.
A membrane with such morphology exhibits a significant
increase in permeability , resulting in death of the cell.
Meanwhile, studies have demonstrated that silver ions
interact with sulfhydryl (-SH) groups of proteins as well
as the bases of DNA leading either to the inhibition of
respiratory processes [15] or DNA unwinding [16].
Inhibition of cell division and damage to bacterial
cell envelopes was also recorded [17] and interaction
with hydrogen bonding processes has been also,
demonstrated to occur [18]. However, the mechanism

depends on both the concentration of silver ions present
and the sensitivity of the microbial species to silver. In the
same time, it was reported that contact time, temperature,
pH and the presence of free water have clear impact on
both the rate and extent of antimicrobial activity [19].
However, in the present study the spectrum of activity
was very wide and the development of resistance was
not recorded. Silver ions clearly do not possess a single
mode of action. They interact with a wide range of
molecular processes within microorganisms resulting in
a range of effects from inhibition of growth, loss of
infectivity to cell death. Another theory explained that
colloidal silver works as a catalyst which can disable the
enzymes that all unicellular bacteria, fungi and viruses use
for their oxygen metabolism. Unlike with antibiotics,
resistant strains have never been known to develop
tell now.

These nontoxic nanomaterials, which can be prepared
in a simple and cost-effective manner, may be suitable for
the formulation of new types of bactericidal materials and
may be solve the problem of the emergence and spread of
in vitro antibiotic resistance.

Nan o silver could be electrically prepared with
low cost, to be applied for external uses only, not for
systemic application and further investigations still
needed.

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Intl. J. Microbiol. Res., 1 (1): 33-36, 2010

In conclusion, nanosilver solution has a powerful
antimicrobial activity against multi drug resistant clinical
Ggram positive and Gram negative bacteria and further
studies still required.

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